Field of the invention
The invention relates to a method and a device for determining a variable that is characteristic of a mass that rests on the seating area of a seat, especially one that is installed in a vehicle.
In modern motor vehicles there is an increasing number of occupant restraint means, such as front airbags, side airbags, knee airbags and curtain airbags. Such occupant restraint means are designed to provide the best possible protection to the vehicle occupants in the event of an accident. This can be achieved in that the deployment area of the occupant restraint means is matched to the particular vehicle occupants in the vehicle. Therefore the risk of injury to babies or small children in the event of an accident can be less if the occupant restraint means do not deploy.
Furthermore, the occupant restraint means should be activated in the event of an accident only where occupants are actually located, the risk of injury to whom is thus reduced. In this way, additional unnecessary high repair costs after an accident can be avoided. For these reasons, it is important to detect the occupancy of a seat of a motor vehicle by an occupant and also to classify these occupants with regard to their characteristics, e.g. with respect to body weight. In this respect, Crash Standard FMVSS 208 is receiving increasing attention. Compliance with it is demanded by numerous vehicle manufacturers. It specifies a classification of the respective vehicle occupants according to their weight, in order in the event of a collision to adapt the control of an occupant restraint means suitably to the identified person as required. To determine the weight of an occupant it is known, for example, from DE 101 601 21 A1, to arrange pressure-sensitive sensor pads in a seating area of the seat and to determine the weight of the occupant from the measured signals from such seat sensor pads.
From U.S. Pat. No. 6,087,598, a weight detection device is known for determining the weight that bears on a vehicle seat of a motor vehicle. First to fourth force sensors are assigned to the vehicle seat, each of which detects forces that act on specific areas of the seating area. The first to fourth force sensors are connected in the area of an underside of the seat cushion underneath the seating area and are also connected to the chassis of the motor vehicle. They are arranged in such a way that they each determine the force acting on the seating area of the seat. In the event of an accident, occupant protection devices such as airbags, head airbags, side airbags or similar, are triggered depending on the measured signals from the sensors.
Furthermore, it is known that an incorrect use of a vehicle seat to which at least one force sensor is assigned that detects the force in the area of the seating area of the seat can lead to a spurious measured signal. If such spurious nature of the measured signal remains undetected, this can lead to an incorrect classification of the occupant sitting on the seat. This then in turn means that in the event of an accident the occupant restraint means is not activated in a manner best suited to the particular occupant. Up until now the positions of the vehicle seat that gave rise to such an incorrect use was stated in the operating instructions.
However, this brings with it the danger that the occupant of the vehicle might not be aware of this statement in the operating instructions and thus be unaware of the dangers associated with such incorrect use of the vehicle seat.